In a portable radio communication device the space for an internal antenna arrangement is limited. With the growing need for greater functionality and better radio channel quality it is often necessary to utilise more than one antenna element in a portable radio communication device, such as a mobile telephone. Because of the limited space in a portable radio communication device, internal antennas tend to be closely spaced. With closely spaced antenna elements unwanted coupling between the antennas can arise.
Low coupling between closely spaced antennas is necessary for various applications. These can be for example: separate RX and TX antenna system which eliminates the need for a diplexer, antenna diversity systems (both receiver and transmitter diversity), antennas for different systems (e.g. GSM-Bluetooth).
In WO 9013152 is described the case of separated RX/TX antennas. WO 9013152 mentions only the case of two antennas of the same type (two similar patches). In WO 9013152 a solution for eliminating the need for a diplexer is provided. Further, it is disclosed that separated transmit and receive antennas are elevated above a grounding surface by a conductive pedestal, wherein the pedestal is placed between the antennas and electrically isolates the antennas.
The above-described document only describes reduced coupling between separated transmit and receive antennas.